This invention is directed to an improvement in an electric soldering iron wherein a heating element having improved heat transfer characteristics is constructed using a blade heater surrounded by a conducting rod which results in an increase in the area of intimate contact between the conducting rod and the heater surface. The increased area of intimate contact between the conducting rod and the heater surface allows more efficient heat transfer than is possible with an assembly having a smaller heat transfer area.
Presently existing soldering irons incorporate a thermal mass in association with a heating element. The heating element is usually a coil of high resistance wire of circular cross section. Because of the circular cross section of the wire, the surface area of the heating element available for heat transfer per unit volume is low. The coiled shape of the heating element further exacerbates this problem by decreasing the surface area in proximity to the thermal mass. Together these two factors greatly limit the amount of surface area available for heat transfer and limit the efficiency of such heat transfer. Consequently, to maintain a specific working temperature a large thermal mass is employed to act as a heat reservoir. The time required to heat the large thermal mass introduces a lag time between heating the element and the soldering iron tip. A corresponding lag time is involved in cooling the iron off.
The presence of the large thermal mass coupled with inefficient heat transfer to the soldering iron tip causes heat transfer to the handle and ultimately to the user's hand, unless sufficient insulation is provided. The large thermal mass and the necessary insulation tend to make such tools bulky and undesirable for extended use or precision applications.
The heating and cooling lag times make it impractical to turn the iron off during intermittent use. Maintaining the soldering iron at its working temperature during idle periods results in higher energy usage. This, in turn, results in higher energy costs.
The large thermal mass also makes it harder to limit heat transfer to the soldering site. This is an important consideration during the assembly of electronic components. These components are usually attached to circuit boards by soldering. Many electronic components which are installed by soldering are damaged or destroyed by heat. Modern practices require an efficient use of circuit board space and consequently electronic components are arranged in high density on circuit boards. Consequently, it is critically important that heat not be transferred from the leads to the body of the electrical component being installed, nor to any adjacent components.